Antiskid control system

ABSTRACT

There is disclosed a control valve arrangement for an antiskid control system which substantially eliminates the abrupt pressure buildup on the brake circuit at the end of each antiskid control cycle when the vehicle wheel has reached a certain reacceleration value. A throttle valve is added to a conventional control valve arrangement so that upon achieving the desired reacceleration value the braking pressure gradually builds up on the brake circuit and thereby eliminates interfering signals in the control signals produced by the antiskid electronic control unit and vibrations of the vehicle itself.

United States Patent 1 Fink et al.

[111 3,731,9fifi 1 May 8, 1973 [54] ANTISKID CONTROL SYSTEM [75]Inventors: Werner Fink; Dieter Kircher; Jutta Mittelbach, all ofFrankfurt. Ger- [21] Appl. No.: 251,898

3,674,317 7/1972 Marigold ..303/2l F Primary Examiner-Richard A.Schacher AttorneyC. Cornell Remsen, Jr. et al.

[57] ABSTRACT There is disclosed a control valve arrangement for anantiskid control system which substantially eliminates the abruptpressure buildup on the brake circuit at the end of each antiskidcontrol cycle when the vehicle Foreign Application Dam wheel has reacheda certain reacceleration value. A May 27. 1971 Germany "P 21 26 39l 2throttle valve is added to a conventional control valve arrangement sothat upon achieving the desired reac- [52] US. Cl ..303/21 F celerationvalue the braking pressure gradually builds [51] Int. Cl. ..B60t 8/06 upon the brake cireuit and thereby eliminates inter- [58] Field Of Search..303/21 F, 21 BE, fering ignals in the control ignals produced by the303/10 antiskid electronic control unit and vibrations of the vehicleitself. [56] References Cited 7 Claims, 2 Drawing Figures UNITED STATESPATENTS 3,674,121 7/1972 Copeland ..303/21 F Mada/02900 VOA/9 5 4 2,#3001 5 \6 l/g/VP l l X 7fi/0ZZ/ Hear/"00m 0 ,1 r Va/z/e onzm/ '7 U U 0Vt? Pump m 1 A st p VO/P flere/emt/on g 6 Sensor /3 BACKGROUND OF THEINVENTION The invention relates to an antiskid control system for motorvehicles which controls the pressure in the wheel brake cylinders duringa braking operation by means of a control member controlled by a controlvalue corresponding to given deceleration values of the wheel and/or ofthe vehicle.

A variety of antiskid control systems are known which operate accordingto different principles. The essential feature of all known antiskidcontrol systems to prevent a locking of the wheels during the braking ofa motor vehicle and, hence, to avoid its undesired consequences whichare hazardous to traffic is to generate a control cycle. The controlcycle includes generating an incipient skid condition control signalshortly before the locking of one or more wheels. This control signal isemployed to reduce the pressure in the brake circuit. Then during thesame control cycle, after the wheel or wheels have reaecelerated to agiven value, the pressure in the brake circuit is permitted to build upagain. Thus, the antiskid control system can begin another controlcycle. The control cycles are preferably adjusted such that throughoutthe braking operation the rotational speed of the wheels in relation tothe translational speed of the vehicle stays within a certain slip rangewhich is favorable for an efficient braking.

Due to the cyclical reduction and buildup of the brake pressure in allknown antiskid systems there results mechanical vibrations which releaseexcessive energies which are especially generated by a previousexcessive brake pressure.

The incipient skid control signal is also subject to a up process duringany succeeding control cycle which renders an exact control difficultdue to the generation of interfering signals by the mechanicalvibrations which are passed on to the control unit or which involve adelay of the following control cycle by special means for the period ofsaid interfering signals. The mechanical vibrations furthermore arehighly disturbing to persons seated in such a vehicle and thereby leadsto uncomfortable driving.

SUMMARY OF THE INVENTION An object of the present invention is toprovide an antiskid system for motor vehicles which is provided withsome means for effective damping of the disturbing mechanical vibrationsand for damping and temporary shortening of the building-up process ofthe incipient skid control signal.

Another object of the present invention to achieve the above mentionedimprovement is to provide a throttle valve actuated by the electroniccontrol unit connected in the pressure medium connection to the brakecircuit to control the build up of pressure in the brake circuit at theend of any control cycle.

A feature of the present invention is the provision of an antiskidcontrol system comprising: a brake circuit including at least twowheels; an electronic control unit coupled to at least one of the wheelsto produce at least a first control signal indicating an incipient skidand a second control signal indicating a given wheel reaccelerationvalue; a source of driver actuated pressure medium; and a control valvearrangement coupled to the control unit and between the source and thebrake circuit, the control valve arrangement being responsive to atleast one of the first and second control signals to control thepressure of the pressure medium coupled to the brake circuit; thecontrol valve arrangement including a throttle valve to provide a slow,smooth build up of pressure of the pressure medium in the brake circuitat the end of each control cycle of the antiskid control system.

Another feature of the present invention is the provision in oneembodiment of the invention of the throttle valve having a firstnormally open position and a second throttle position. The throttlevalve is connected in the direct pressure medium connection between thepressure medium source and the wheel brake circuit. In the firstposition of the throttle valve 'the passage cross section of thethrottle valve corresponds to the passage cross section of the brakecircuit. In the second or switched position of the throttle valvethepassage cross section of the throttle valve has a certain throttlingcross section.

Still another feature of the present invention is that where the buildup of pressure in the brake circuit is controlled by means of an inputvalve connected in the pressure medium connection between the pressuremedium source and the wheel brake circuit and that where the pressurereduction is controlled by means of an output valve connected in abranch of the pressure medium connection, said branch leading to thereservoir, the throttle valve will be connected in series with respectto the input valve, said input valve having a first normally openposition and a seeond closed position.

A further feature of the present invention is that the above mentionedinput valve and throttle valve are simultaneously switched to theirsecond positions. When returning to their first positions, the return ofthe throttle valve to its first position will be delayed by a certainamount relative to the return of the input valve to its first position.This delayed return of the throttle valve to its first position will bedetermined by the pressure difference between the pressure of thepressure medium from the source and the pressure as it builds up in thebrake circuit, said pressure difference being zero or some given smallvalue to accomplish the objects of the pressure invention.

Sill a further feature of the present invention is the provision inanother embodiment of the throttle valve having a first normal throttleposition and a second closed position. This throttle valve is connectedin the pressure medium connection between the pressure medium source andthe pressure medium actuating chamber which effects the building-up andreduction of a separating valve. The throttle valve in its firstposition controls the movement of the throttle valve to provide theslow, smooth build up of pressure of the pressure medium in the brakecircuit.

BRIEF DESCRIPTION OF THE DRAWING Above-mentioned and other features andobjects of this invention will become more apparent by reference to thefollowing description taken in conjunction with the accompanying drawingin which:

FIG. 1 shows a schematic illustration of an antiskid system inaccordance with the principles of the present invention having input andoutput valves to control the build-up and the reduction of the pressureof the brake pressure medium; and

FIG. 2 shows a schematic illustration of an antiskid system inaccordance with the principles of the present invention incorporated ina brake system of the pumpaccumulator type and having a separating valveto control the build-up and the reduction of the pressure of the brakepressure medium.

DESCRIPTION OF THE PREFERRED EMBODIMENT At first the embodiment as perFIG. 1 will be described.

Referring to FIG. 1, pressure medium connection 2 leads from modulationvalve 1, such as a power assisted brake or brake booster arrangement, tothe brake circuit including at least two wheel brake cylinders of brakes3 provided at the vehicle wheels 4. Upon actuation by means of brakepedal BP, modulation valve 1 will pass on the pressure of accumulator 14charged by pump 9 via accumulator charging valve 13, said pressurehaving been modulated in accordance with the actuation pressure Inputvalve 5 is connected in pressure medium connection 2 in a manner knownper se. In its rest or first position, input valve 5 opens theconnection between modulation valve 1 and the wheel brake circuit. Inits switched or second position, input valve 5 will interrupt thisconnection. Between input valve 5 and the wheel brake circuit branch 6is provided which leads from pressure medium connection 2 into reservoir8 via output valve 7 which in its rest or first position is closed andwhich in its switched or second position is open. From reservoir 8 pump9 will deliver the pressure medium back into accumulator 14 whenrequired through charging valve 13.

Since to a considerable extent the above-mentioned mechanical vibrationsand interfering signals are the result of too abrupt a new build-up ofbrake pressure in the brake circuit during the last phase of a controlcycle, the invention provides for the connection of throttle valve 10 inpressure medium connection 2. Throttle valve 10 is connected in serieswith input valve 5 and modulation valve 1. Throttle valve 10 in theembodiment of FIG. 1 has a first open position and a second throttleposition. In its rest or first position throttle valve 10 ensures acompletely free passage of pressure medium therethrough while in itssecond or switched position valve 10 is provided with a throttlingcross-section which corresponds to the requirements of the system toachieve mechanical vibration and interfering signal reduction.

Input valve 5, output valve 7 and throttle valve 10 areelectromagnetically operated by the output signals of electronic controlunit 11 which are generated in accordance with the measured values ofdeceleration by sensor 12 disposed at wheel 4 and communicating with theinput of control unit 11.

With regards to the process of generating dependent output signals incontrol unit 11 there exist in the prior art many alternativearrangements. Control unit 11 may be any known circuit that provides afirst control signal indicative of an incipient skid, a second controlsignal indicative of the wheel achieving a given reacceleration valueand a third control signal, employed only in FIG. I, indicative of adeceleration value between the deceleration values represented by thefirst and second control signals.

In the first position of valves 5, 7 and 10 pressure may be built up inthe wheel brake cylinder of brake 3 via modulation valve 1. If due toexcessive brake pressure wheel 4 tends to lock the first control signalof control unit 11 will cause valves 5, 7 and 10, to switch to theirsecond position. The pressure medium in the section of the pressuremedium connection 2 separated from the modulation valve 1 and connectedwith the wheel brake circuit will expand through branch 6 and valve 7into reservoir 8. According to the majority of the suggested controlprocesses output valve 7 will be returned into its initial or firstposition as soon as the deceleration of wheel 4 has reduced by a certainamount. This is accomplished by the third control signal from unit 11.The brake pressure in the brake circuit will be kept at this reducedlevel for a certain period, namely, until wheel 4 reaccelerates to agiven value. While in the known antiskid systems of this type, withoutthrottle valve 10, the pressure in the brake circuit will be abruptlyrestored to its old value by means of input valve 5 at the cost of theabove-mentioned disadvantages as soon as a certain reacceleration ofwheel 4 is achieved. In the inventive antiskid system disclosed hereinthe pressure increase in the brake circuit and, hence, the newdeceleration of wheel 4 is brought about in a delayed and smoothermanner due to the action of throttle valve 10. Upon achieving of theabovementioned reaccleration of wheel 4 input valve 5 returns into itsfirst position in the known manner and throttle valve 10 will stay inits second position for a certain period of time, or until there resultsa certain pressure difference across throttle valve I0. It is only whenthe pressure in the brake circuit has gradually achieved the pressuredetermined by modulation valve 1 that throttle valve 10 will switch intoits initial or first position.

FIG. 2 shows the schematic illustration of the inventive control valvearrangement including a throttle valve in an antiskid system and brakesystem of another type.

Pump 21 sucks pressure medium from reservoir 20 and charges accumulator23 via accumulator charging valve 22. Accumulator 23 is connected withthe input of modulation valve 24, such as a power assisted brake orbrake booster arrangement, operated by means of brake pedal BP. Theoutput of modulation valve 24 is connected by pressure medium connection27 with the wheel brake cylinder of brake 25 disposed at wheel 26.Separating valve 29 is connected in connection 27. Valve 29 includes apressure medium input 29a and a pressure medium output 2% separated by avalve member 29c and valve seat 29d. Member 29c is moved mechanicallyand/or by pressure medium. As illustrated plunger 28 in chamber 31 ismechanically connected to member 290. Pressure medium is coupled intochamber 31 by control input 2% and removed from chamber 31 by controloutput 29]". Since various forms of separating valves are known in theprior art, one embodiment of separating valve 29 has b-en shown only inoutline.

Plunger 28 now is held in its initial or first position by means of aspring 30. When plunger 28 is in its initial position, the pressuremedium connection 27 between modulation valve 24 and the wheel brakecircuit has the smallest volume possible. Front surface 28a of plunger28 keeps valve member 290 in lifted position with regard to valve seat29d. Chamber 31, in which spring 30 is located, which is confined byrear surface 28bof plunger 28. Control output29 f of chamber 3i isconnected with reservoir by means of output valve 32 which in its restor first position is closed and which in its second or switched positionis open. Furthermore, chamber 31 is connected with either the output orthe input of the modulation valve 24 by means of control input 29e andthrottle valve 33 having as its first or rest position a throttleposition and as its second or switched position a closed position.Output valve 32 and throttle valve 33 are electromagnetically operatedby means of the first and second control signals of electronic controlunit 34 whose input is connected with deceleration sensor 35 disposed atwheel 26. Control unit 34 generates first and second control signalswhich are identical to the first and second control signals generated bycontrol unit 11 of FIG. 1.

The accumulator pressure acting on the input of modulation valve 24 willbe passed on modulated through pressure medium connection 27 andseparating valve 29 in its first position to the wheel brake circuitupon the onset of a braking operation.

The pressure built up in the chamber 31 of valve 29 through throttlevalve 33 being in its first position will be applied to surface 28b ofplunger 23. This pressure will cooperate with the force of spring to actagainst the brake pressure acting on front surface 28a of plunger 28 andthereby maintain valve 29 in its first position. If wheel 26 tends tolock output valve 32 and throttle valve 33 will be switched into theirsecond position by means of the first control signal emitted by controlunit 34. Thus, pressure medium will leave chamber 31 and will flow intoreservoir 20. No additional pressure medium will be supplied to chamber31 since throttle valve 33 is closed. The brake pressure acting on frontsurface 28a of plunger 23 will displace plunger 28 against the reducedpressure of chamber 31 so that valve member 29c is closed against valveseat 29d. By this action the volume of the pressure medium connection 27between separating valve 29 and the wheel brake circuit will beincreased and, hence, the pressure medium is expanded. Output valve 32and throttle valve 33 will return to their initial or first positionupon occurrence of the second control signal from control unit 34. Thepressure in the brake circuit is kept constant until throttle valve 33returns into its rest or first position. Because of the throttledpressure increase in chamber 31 as a result of valve 33, plunger 28 willslowly and smoothly return into its initial or first position and openthe separating valve 29.

Due to the throttled pressure increase in chamber 31 of valve 29 ascontrolled by throttle valve 33, plunger 28 will not abruptly returninto its initial position. Thus, disturbing mechanical vibrations willbe effectively damped and the building-up process of the incipient skidcontrol signal will be damped and shortened.

While we have described above the principles of our invention inconnection with specific apparatus it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim: 1. An antiskid control system comprising: a brake circuitincluding at least two wheels; an electronic control unit coupled to atleast one of said wheels to produce at least a first control signalindicating an incipient skid and a second control signal indicating agiven wheel reacceleration value; a source of driver actuated pressuremedium; and a control valve arrangement coupled to said control unit andbetween said source and said brake circuit, said control valvearrangement being responsive to at least one of said first and secondcontrol signals to control the pressure of the pressure medium coupledto said brake circuit; said control valve arrangement including athrottle valve to provide a slow, smooth buildup of pressure of thepressure medium in said brake circuit at the end of each control cycleof said antiskid control system. 2. A system according to claim 1,wherein said throttle valve has a first normally open position and asecond throttle position, said throttle valve responding to said firstcontrol signal to switch from said first position to said secondposition and said throttle valve switching from said second position tosaid first position at a time delayed with respect to the generation ofsaid second control signal. 3. A system according to claim 2, whereinsaid delayed time is determined by the pressure buildup of said pressuremedium in said brake circuit to a given valve of pressure differencewith respect to the pressure of said pressure medium from said source.4. A system according to claim ll, wherein said throttle valve has afirst normal throttle position and a second closed position, saidthrottle valve responding to said first control signal to switch fromsaid first position to said second position and to said second controlsignal to switch from said second position to said first position. 5. Asystem according to claim ll, wherein said control valve arrangementincludes said throttle valve having an output and an input connected tosaid source, said throttle valve having a first normally open positionand a second throttle position, said throttle valve responding to saidfirst control signal to switch from said first position to said secondposition and said throttle valve switching from said second position tosaid first position at a time delayed with respect to the generation ofsaid second control signal, and an input valve having an input connectedto said output of said throttle valve and an output connected to saidbrake circuit, said input valve having a first normally open positionand a second closed position, said input valve responding to said firstcontrol signal to switch from said first position to said secondposition and to said second control signal to switch from said secondposition to said first position, said delayed time of switching saidthrottle valve with respect to the actuation of said input valve by saidsecond control signal providing said slow, smooth buildup of pressure ofthe pressure medium in said brake circuit. 6. A system according toclaim 5, wherein said control unit produces a third control signalindicating a deceleration intermediate said incipient skid and saidgiven wheel acceleration; and said control valve arrangement furtherincludes an output valve having an input coupled to said brake circuitand an output to return said pressure medium to said source, said outputvalve having a first normally closed position and a second openposition, said output valve responding to said first control signal toswitch from said first position to said second position and to saidthird control signal to switch from said second position to said firstposition. 7. A system according to claim 1, wherein said control valvearrangement includes a pressure medium controlled separating valvehaving an input and an output connected between said source and saidbrake circuit, a pressure medium control input and a pressure mediumcontrol output, said separating valve having a first normally openposition and a second closed position, said throttle valve having aninput connected to said source and an output connected to said controlinput, said throttle valve having a first normal throttle position tomaintain said separating valve in its first position and a second closedposition, and

an output valve having an input coupled to said control output and anoutput to return said pressure medium to said source, said output valvehaving a first normally closed position to cooperate with said throttlevalve in said first position to maintain said separating valve in itsfirst position,

both of said output and throttle valves responding to said first controlsignal to switch from their first position to their second position andas a result switch said separating valve to its second position andresponding to said second control signal to switch from their secondposition to their first position and as a result of the throttlingeffect of said throttle valve provide a slow, smooth switching of saidseparating valve from its second position to its first position andthereby provide said slow, smooth buildup of pressure of the pressuremedium in said brake circuit.

1. An antiskid control system comprising: a brake circuit including atleast two wheels; an electronic control unit coupled to at least one ofsaid wheels to produce at least a first control signal indicating anincipient skid and a second control signal indicating a given wheelreacceleration value; a source of driver actuated pressure medium; and acontrol valve arrangement coupled to said control unit and between saidsource and said brake circuit, said control valve arrangement beingresponsive to at least one of said first and second control signals tocontrol the pressure of the pressure medium coupled to said brakecircuit; said control valve arrangement including a throttle valve toprovide a slow, smooth buildup of pressure of the pressure medium insaid brake circuit at the end of each control cycle of said antiskidcontrol system.
 2. A system according to claim 1, wherein said throttlevalve has a first normally open position and a second throttle position,said throttle valve responding to said first control signal to switchfrom said first position to said second position and said throttle valveswitching from said second position to said first position at a timedelayed with respect to the generation of said second control signal. 3.A system according to claim 2, wherein said delayed time is determinedby the pressure buildup of said pressure medium in said brake circuit toa given valve of pressure difference with respect to the pressure ofsaid pressure medium from said source.
 4. A system according to claim 1,wherein said throttle valve has a first normal throttle position and asecond closed position, said throttle valve responding to said firstcontrol signal to switch from said first position to said secondposition and to said second control signal to switch from said secondposition to said first position.
 5. A system according to claim 1,wherein said control valve arrangement includes said throttle valvehaving an output and an input connected to said source, said throttlevalve having A first normally open position and a second throttleposition, said throttle valve responding to said first control signal toswitch from said first position to said second position and saidthrottle valve switching from said second position to said firstposition at a time delayed with respect to the generation of said secondcontrol signal, and an input valve having an input connected to saidoutput of said throttle valve and an output connected to said brakecircuit, said input valve having a first normally open position and asecond closed position, said input valve responding to said firstcontrol signal to switch from said first position to said secondposition and to said second control signal to switch from said secondposition to said first position, said delayed time of switching saidthrottle valve with respect to the actuation of said input valve by saidsecond control signal providing said slow, smooth buildup of pressure ofthe pressure medium in said brake circuit.
 6. A system according toclaim 5, wherein said control unit produces a third control signalindicating a deceleration intermediate said incipient skid and saidgiven wheel acceleration; and said control valve arrangement furtherincludes an output valve having an input coupled to said brake circuitand an output to return said pressure medium to said source, said outputvalve having a first normally closed position and a second openposition, said output valve responding to said first control signal toswitch from said first position to said second position and to saidthird control signal to switch from said second position to said firstposition.
 7. A system according to claim 1, wherein said control valvearrangement includes a pressure medium controlled separating valvehaving an input and an output connected between said source and saidbrake circuit, a pressure medium control input and a pressure mediumcontrol output, said separating valve having a first normally openposition and a second closed position, said throttle valve having aninput connected to said source and an output connected to said controlinput, said throttle valve having a first normal throttle position tomaintain said separating valve in its first position and a second closedposition, and an output valve having an input coupled to said controloutput and an output to return said pressure medium to said source, saidoutput valve having a first normally closed position to cooperate withsaid throttle valve in said first position to maintain said separatingvalve in its first position, both of said output and throttle valvesresponding to said first control signal to switch from their firstposition to their second position and as a result switch said separatingvalve to its second position and responding to said second controlsignal to switch from their second position to their first position andas a result of the throttling effect of said throttle valve provide aslow, smooth switching of said separating valve from its second positionto its first position and thereby provide said slow, smooth buildup ofpressure of the pressure medium in said brake circuit.